Sorbitan esters have been used for many years as surface active agents, having emulsifying, dispersing, wetting and/or solubilising properties in a wide range of applications such as personal care, cleaning, general industrial, food, and many others. In particular, sorbitan esters have been used as emulsifiers in personal care applications, for example skin care, sunscreens, toiletries, decorative cosmetics, perfumes and fragrances.
Commercial production of sorbitan esters normally involves the reaction of sorbitol with fatty acids or derivatives thereof, and results in a complex mixture of products including sorbitol mono- di-, tri-, and higher esters, sorbitan mono-, di-, and higher-esters, isosorbide mono-, and di-esters, and non-esterified sorbitol, sorbitan and isosorbide. The concentrations of the aforementioned individual components can vary, but sorbitan esters are the main components. There can be significant amounts of isosorbide esters present, but sorbitol esters are normally present at very low concentrations. The number of carbon atoms present in the hydrophobe of the sorbitol/sorbitan/isosorbide esters is dependant upon the particular fatty acid(s) employed in the reaction, and the average number thereof will be substantially the same for all of the components.
Current commercially available sorbitan esters are effective emulsifiers in many applications, but there is still a requirement to improve the properties thereof, particularly in personal care applications, such as flexibility of use, improved water resistance, smooth and light skin feel, and spreading properties. Often an additional co-emulsifier is required to be used with sorbitan esters, and there would be significant advantages if a sorbitol based self-emulsifying system could be developed, i.e. without the need for a co-emulsifier, particularly one capable of forming liquid crystals in water, and especially in oil in water emulsions.